The most typical private sewage disposal system is the septic tank system. The typical septic tank system consists of a leaching bed also called a tile field connected to a concrete septic tank connected to the waste outlet pipe of a building.
The tile bed consists of a series of perforated pipes laid on a bed of stone or gravel in trenches and covered by earth. This series of perforated pipes are connected to an unperforated pipe called the header. The header is connected by pipe to the outlet side of the septic tank.
The septic tank is most commonly made of concrete but can also be plastic or fibreglass. Some older septic tanks are made of steel and very old ones are cribs made of wood. The typical current standard septic tank is a two compartment concrete tank with inlet and outlet baffles on the inside of the tank. These tanks also have concrete manhole access lids ("covers"). The septic tank is installed in the ground and is covered by eighteen inches to two feet or more of earth. The outlet side of the septic tank is connected to the header pipe of the tile field and the inlet side of the septic tank is connected to the plumbing waste pipe of a building.
The septic tank system is more than just a waste disposal system. It is also a waste treatment system and when properly installed and maintained it is a very effective treatment system.
The waste that is disposed of in a septic tank system contains dangerous bacteria, viruses, parasites and substances such as detergents, soaps, greases, food particles, cleaners, bleaches, ammonia, polishes, solvents, insect sprays, various body fluids, faeces, urine, and other offensive or putrescible substances. The waste requires careful disposal in order to protect human health and the natural environment. The microorganisms in the waste such as bacteria, viruses and parasites can cause serious illnesses in humans and therefore if allowed to escape untreated can pose a serious public health threat. Some of these same microorganisms can also cause illness in animals such as livestock. Inadequately treated sewage should not be allowed to pond on the surface of the ground, to flow into open ditches, to back up into basements or foundation drainage systems, to drain directly or indirectly into streams, lakes or other bodies of water or to contaminate ground water aquifers.
Most municipalities in North America have legislation and associated programs in place to monitor and approve the installation of private sewage disposal systems. However, once installed the ongoing maintenance of the private sewage disposal system is usually left up to the individual owner. In the province of Ontario alone 20,000 new septic tank systems are installed each year. Ninety percent of farms in Ontario rely on private water supplies and private sewage disposal systems.
Many studies including those carried out in the Great Lakes Basin in connection with RAPs (Remedial Action Plans) and those carried out in Ontario in connection with CURB (Clean Up Rural Beaches) plans have pointed to malfunctioning septic tank systems as a source of at least some of the contamination found in our surface waters.
Contamination of ground water including well water for drinking and for livestock watering also points to malfunctioning septic tank systems as a source.
A 1992-93 CURB Plan in Eastern Ontario determined that malfunctioning septic tank systems contributed from three trillion Faecal Coliform bacteria annually for the Trent River to over seven trillion Faecal Coliform bacteria annually for the Napannee River.
A properly installed and maintained septic tank system is not a pollution problem but a malfunctioning system can certainly create a significant public health hazard and environmental health hazard.
The first chamber of a septic tank provides treatment of the waste via the action of anaerobic bacteria. The bacteria naturally in the waste breaks down the waste causing solids or sludge to settle to the bottom of the tank and lighter material "the scum" to float on the surface. The size of a septic tank is important as the waste needs to be retained within the tank for at least 24 hours before it passes into the leaching pipes. During the 24 hours of retention time the waste is broken down into sludge, scum and effluent. The effluent which is the liquid between the sludge and the scum layer passes into the second chamber of the tank and from here it trickles out the outlet pipe into the leaching pipes. The baffles in the tank help to prevent the scum from passing through the tank. At this point the effluent is actually quite clear.
The pipes of the leaching bed distributes the effluent throughout the tile field. The effluent escapes through the perforations in the bottom of the pipe into the gravel or stone bed. As the effluent travels through the stone it is further treated by the action of aerobic bacteria. This action assists in destroying the harmful disease causing bacteria and other pathogenic microorganisms. Over time an organic mat actually forms which further improves the treatment efficiency of the system. The effluent continues to travel beyond the gravel bed and through the soil where the remaining microorganisms are filtered out or are acted upon by soil bacteria. This last stage requires about three feet of unsaturated soil to insure that the effluent reaching the ground water table is microbiologically safe.
A problem occurs when the sludge in the tank builds up over time and the scum layer gets thicker until the two meet in the middle. When this happens there is no capacity left to allow the minimum 24 hours of retention time and no room for the clear effluent to be produced. The treatment quality of the tank is greatly diminished and the sludge and the scum start to get into the second chamber and then into the leaching pipes. When this happens these solid particles plug up the leaching pipes and then there is no adequate distribution of the effluent and no proper treatment of the waste in the tile field.
When the tile field gets plugged up the effluent which can get through the soil is not adequately treated and therefore contaminates the ground water. The effluent which can not get through the soil backs up to the surface of the ground. Once on the surface of the ground the highly contaminated effluent finds its way to surface water sources, especially with the assistance of rainfall.
To prevent this problem routine maintenance of the septic tank requires that the septic tank be pumped out when the bottom of the scum layer is within 3 inches of the bottom of the baffle or outlet fitting, or when the surface of the sludge accumulation is within 18 inches of the baffle or outlet fitting. A septic tank could be pumped out on a regular basis such as every two or three years. This method of maintenance may exclude the need to measure the septic tank contents on an annual basis. However the waste of every household is not the same. Some tanks may need to be pumped every year or sooner and some may only need to be pumped every five years. It would certainly be a waste of money to pump a septic tank out when there is no need to. Also there is a need for proper disposal of the contents pumped from the septic tank therefore it is also in the interests of the environment not to create this additional waste material unless it is absolutely necessary.
It is a fairly significant chore for the average private sewage disposal system owner to measure the contents of their septic tank and certainly so on a regular basis. Probably the thought of carrying out the task only to find that pumping is not needed at that time would be a reason many people may not go to the trouble.
The steps involved in determining the need for pumping are difficult and unpleasant. The usual steps entail:
determining exactly where the septic tank is buried in the ground (usually requires probing with a steel rod); PA1 once the tank itself is located, determining the orientation of the tank in order to find the correct access cover (may also require probing with a steel rod, being careful not to damage the inlet or outlet pipes); PA1 removing overlying sod with as little disturbance as possible and then the soil over the proper location (usually has to be done manually with a spade shovel); PA1 removing the concrete cover without injury to one's back (concrete manhole covers usually weight about 75 pounds and fit quite tight especially after being buried in the ground for a few years); PA1 reaching into the septic tank with a yard stick or similar measuring device to measure the amount of sludge and scum; and, PA1 if the tank does need to be pumped, temporarily covering the hole for safety reasons while awaiting arrival of a septic tank pumper.
It is for these reasons that most private owners are not motivated to carry out routine inspections of their septic tanks and to have the tanks pumped out when the time is due.
Unfortunately most people are not aware of the consequences of not inspecting and pumping their septic tanks and they are not aware until it is too late that corrective action for a malfunctioning system is usually a very costly replacement of the entire tile field not to mention the cost of the damage to the environment and maybe even their own health if it is their drinking water supply that becomes contaminated.